Reporter: Every hotel has its rules, but here at the elegante they're actually written in stone. A 10 commandments monument near the lobby reminds all -- "thou shalt not kill." But somebody broke that rule. And greg fleniken paid the price. Uh, you know, there should be more people in this world like, uh, greg fleniken. Reporter: Unfortunately, he was, he was stolen from his wife. Yeah, exactly. Reporter: By the time private investigator ken brennan rolls into town, the body is cold and the leads are even colr. Investigations are like a puzzle. And, uh, a puzzle has many pieces. But every one, each and every one of those pieces has to fit, and they have to fit perfectly. Reporter: While the whodunit remains a mystery, the private investigator hones in on "the where" and "the when." This happened between 8:30 and 9:00 o'clock at night. He loved the room ice cold, his wife always said that, you know, he liked it like a meat locker. Reporter: It was fleniken himself who -- while watching "ironman 2" and making some popcorn in the microwave -- tripped the circuit breaker. Part of the hotel goes dark. I said, when they came in to reset the circuit breaker, I'm sure they shut everything down, to reset the circuit breaker, so they shut off the air conditioning." Reporter: It had to have happened in that window, right after the maintenance guys left. He was killed before he realized that the room got warm. Reporter: Because he was so adamant about keeping the room freezing cold. Ice cold. Exactly. Reporter: And when detectives discovered that body, the room was broiling. No one had turned that air conditioner back on. Brennan theorized that perhaps the hotel blackout could have led to an argument between fleniken and another guest who might have been ticked off. He must've had a confrontation. I said, "we're gonna find out that it was probably the two guys next door." Reporter: Brennan knows the living tell all sorts of stories. I know if the guys next door had anything to do with this, they won't keep it to themselves. They will tell their other co-workers. Reporter: He goes to find the co-workers of the men staying next door. No one knows anything. Except a supervisor, who says he does recall hearing some story about a gun going off. The details don't seem to match the elegante killing, but brennan perks up. Any time anybody tells a story, nobody remembers, but when somebody mentions something about a gun, that's the part they'll remember. The gun. They don't remember anything else, but they remember the gun. Reporter: More than eight months into the case, it's the first time anyone has ever mentioned anything about a gun. Detective apple thought that was just crazy, but ken brennan said, "no we have to go check this out." Reporter: They return to the scene of the crime, room 348. And they saw this indentation in the wall. Reporter: In fact, maintenance records show the wall in 348 had been repaired, but the indentation was noticeable in those crime scene photos. You notice some patching on the wall. So, I said it's too big for a bullet hole, but let's see what it says on the other side. Reporter: So now, you're going into room 349. Correct. Reporter: Where the electricians were hanging out. Let's go from the other side of the wall, put the dowel through the wall from where the bullet would've came from. Put a laser on the end of that, and see what we have. Reporter: Well you saw that laser. Right. Reporter: Go through the wall. Right across the top of the bed, right at the head of his pillow where he had been laying. Straight at the bed. Reporter: Clear shot. Clear shot. I said, "scott, this was shot." At that point, we know exactly what happened. Reporter: You think somebody must have shot the gun through that wall. Has that private eye reached too far. The autopsy never mentioned anything about a gunshot wound. The medical examiner listing cause of deaths as blunt force trauma. The medical examiner has been doing it a long time, he's done good work, he's trusted. What he says is gospel. Reporter: They have to explain to the medical examiner their rewriting his gospel. So you tell him your idea, and at first, he's not buying it. He's not buying it at all. And, you know, he picked up on it right away, and he says, "hey." He says, "this -- this guy was not shot. This guy was beaten to death." Reporter: But brennan keeps sliding the proof toward the medical examiner. All of the photos making his case that all of that internal damage from the groin right up through the heart was caused not by a kick from someone, but from a bullet. I go, "doc. That's a bullet hole. Come on." And he just looked, and he goes, Reporter: His mind was changed. At least he was man enough that when we did show him physical evidence that was contrary to what he believed, that he was man enough to say, "okay, you're right." Reporter: And while the cause of death has suddenly changed, will these men change their stories? I don't know nothing, like i said. You don't think that we know the story, that we don't know what the hell went on here? Of course we know.

This transcript has been automatically generated and may not be 100% accurate.

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